Amplitude modulation atomic force microscopy (AM-AFM) has been very successful for imaging with high spatial resolution inorganic as well as soft materials such as polymers, living cells and single biomolecules in their natural environment [1]. The ability of AM-AFM to separate topography from compositional contrast is probably one its main advantages. Compositional mapping is achieved by recording simultaneously the oscillation amplitude and the phase lag between the external excitation of a vibrating tip and its response in the vicinity of the surface...